Consider a man of some qualifications and pay. A woman A as qualified as him earn less. A woman B who earn as much as him are more qualified. But the slope of the qualifications-wages line between woman A and woman B goes the wrong way for qualifications to be positively correlated to wages - the less qualified woman earns more!

You have a typo here, I think- suppose the man has qualification 2 and salary 2. A has qualification 2 and earns 1, but B has salary 2 and qualification 3. The line is positive. If B has salary 2 and qualification 1 (i.e. the man is more qualified, not the woman more qualified) then this matches the description and the line is negative.